Tonight I installed a Sony HU in a friend'* 1999 Bonneville SSEI. The stock one was a Delco unit and I don't know if there is an amp or not. We used an aftermarket harness adapter to keep the wiring as stock as possible but upon powering the new radio up for the first time the unit was operating and getting a radio signal but no sound to the speakers.
I did a little research and found that the 2nd harness that has only 1 orange wire was the key to this problem, and it needs a 12 volt signal so I wired it into the power antenna lead. Everything worked fine.
On my way home my friend called to say that he went for a drive and now the horn starts honking when starting the car and when shutting it off. Also, his digital compass display on the left side of the instrument cluster is not working.
Please, any ideas? Does that single orange lead need to be connected elsewhere?

First things first, disconnect the new HUD and try to duplicate the horn going off while starting and shutting off. If it goes away, we need to figure out what happened during the install. I have schematics from Alldata that can help us out.

take it apart and look for chafed wires, they are thin and tight. that orange one allmost broke all the way through when i took my radio out to fix the display light

Thanks for the replies, guys. He called me today and told me that the problem is not occurring today, so we'll see how it goes. Is it possible the body control module got a little confused or something, and sitting over night somehow "cured" the problem? I realize that sounds a little far-fetched, but...